The invention relates to a circuit arrangement for the operation of at least two electric machines with a different inductance requirement being placed on a converter power section.
In the machine tool industry, specifically in machining centers, there is increasingly the need to operate at least two spindles with the corresponding drives using one power section. In this case, different spindles, which are each driven by an electric machine, are used for machining, for example roughturning and fine machining/planing. The replacement of the spindles generally takes place via a tool robot. In this case, the two spindles driven by synchronous motors are intended to be operated in an inexpensive manner using one power section.
The electric machines are often in the form of synchronous motors. Owing to the need to operate the electric machines at a certain power in the field weakening range, a choke inductance is required as a series inductor (series inductance), which needs to be matched to the inductance of the respective electric machine. Inexpensive circuitry for the choke inductances and the electric machines for both operating cases is therefore desired.
In the event of failure of the power section/actuating drive (pulse suppression) in the case of a maximum speed of the electric machine, said electric machine acts as a generator. In this case, a generator voltage (EMF) of up to several kV can be produced, which can damage or destroy other components in the drive circuit. A voltage protection module VPM limits this voltage, for example to a maximum of 830 V, by virtue of the fact that the three phase lines are short-circuited in the corresponding case. The circuit for driving the electric machines including the associated choke inductances therefore needs to be selected in such a way that the generator voltage is safely limited even in the event of a voltage failure.